In HVAC units and systems, condenser fans are used such as in water chillers to reject heat from refrigerant flowing through the system. Heat can be rejected from the refrigerant, for example to some other fluid such as air or water, or to ambient. Control of the condenser fans can be operated to minimize head pressure on the compressor(s), such as by maximizing the number of fans running in units/systems that use fixed speed fans. Such control can maximize chiller efficiency, such as at full load.